Propane used in liquefied petroleum gas (LPG), thermal power generation fuel, etc. is commonly purified industrially by fractional distillation of the petroleum as raw material. Consequently, propane currently in common use contains at least one of ethane and propylene, at least one of isobutane and normal butane, water, nitrogen, oxygen, and carbon dioxide as impurities, and the purity thereof is low and varies at a level on the order of 98.5% by volume.
However, the need for high-purity propane having a low concentration of impurities has increased in recent years. For example, there is a growing demand for propane as a raw material of high-withstand voltage silicon carbide (SiC) semiconductors. In order to realize this high level of withstand voltage performance of silicon carbide, the concentration of each impurity present in propane is required to be less than 1 ppm by volume, and in particular the concentration of nitrogen is required to be less than 0.1 ppm by volume.
Therefore, it is considered to distill high-purity propane from low-purity propane that is currently in common use having a purity of about 98.5% by volume. However, in the case of distilling high-purity propane from low-purity propane, the scale of the equipment becomes large and a large amount of energy is required. In the case of containing propylene in particular as an impurity, since the difference in boiling points between propane and propylene is small, the purification by distillation becomes difficult. Furthermore, a method of selectively absorbing propylene by an aqueous solution containing silver nitrate is known in order to separate propylene that is a member of olefins from propane that is a member of paraffins (see Patent Document 1). In this method, however, since propane, ethane, isobutane, and normal butane that are members of paraffins cannot be separated from each other, purification to high-purity propane cannot be achieved even if this method is employed.